This invention relates to mono-directional flow valving for medical and laboratory apparatus. In particular, the present invention concerns a medical check valve which has a predetermined cracking pressure while ensuring fluid flow through the valve in only one direction.
Check valves are widely used in medical systems to prevent reverse fluid flow, e.g., in catheters and intravenous lines. U.S. Pat. No. 3,601,151 to Winnard shows a check valve assembly employing an elastomeric sock member which surrounds the end of the cylindrical stem. The cylindrical stem passes fluid through a centrally disposed axial bore. In its neutral configuration, the elasticity of the sock member seats the sock on the cylindrical surface of the stem thereby preventing fluid flow through the stem. Upon sufficient fluid pressure within the stem bore, the elastic sock expands to permit the passage of the fluid between the sock and the outside of the stem. Reverse pressure forces the sock against the cylindrical surface and this prevents flow in the reverse direction. However, if the reverse pressure is high, the sock member may be subject to rupture. Because the sock and stem must be specially sized for each particular cracking pressure, this type of valve is expensive to manufacture where valves of different cracking pressures are desired. Also, the size variation of the components due to manufacturing tolerances prohibits the production of valves from standard components having a common cracking pressure.